1. Field of the Invention
The present invention relates to a disc driving apparatus for driving a disc such as a CD and DVD.
2. Description of the Related Art
A disc driving apparatus includes a turntable on which a disc is to be placed and a clamping member for holding the disc between the turntable and the clamping member with a magnetic attracting force. In addition, there is provided a cam mechanism, which has a cam and a cam follower, for causing a relative movement between the turntable and the clamping member to move any one of them away from another thereof or move them closer to each other. More specifically, when the disc is to be loaded on the turntable, the cam is operated to turn in a direction to move the turntable and the clamping member away from each other through the cam follower. Then, an empty disc tray is moved away from between the turntable and the clamping member. After the disc is placed on the empty disc tray, the disc moves toward a predetermined position between the turntable and the clamping member. In this stage, the cam is operated to turn in the opposite direction to move the turntable and the clamping member close to each other. When the disc placed on the disc tray enters the predetermined position between the turntable and the clamping member, the disc tray stops moving. At the same time, the turntable and the clamping member are attracted to move close to each other, thus holding the disc between them. The turntable holds the disc and rotates so as to read information recorded on the disc by means of a pickup or record information thereon.
With respect to the cam of the cam mechanism of the conventional disc driving apparatus, a cam provided with a guide groove is usually used so that the cam follower is received in the guide grove of the cam. The above-mentioned cam follower is connected to any one of the clamping member and the turntable. When carrying out a lodging or dislodging operation of the disc, a reciprocating motion of the cam with the guide groove causes a relatively sliding motion of the cam follower in the guide groove of the cam so as to move the turntable close to the clamping member or move the former away from the latter.
The guide groove of the cam of the conventional cam mechanism is provided in the form of a slot having a constant width so that the opposite guide surfaces thereof are in parallel with each other, thus preventing the cam follower from jouncing in the guide groove. In addition, an angle between the horizontal line and each of the opposite guide surfaces of the guide groove is relatively larger, so as to provide a rapid clamping operation of the disc. As a result, heavy load is applied to a motor for driving the disc to cause problems, when moving the clamping member and the turntable away from each other. Especially, a recent demand for fast reading and writing requires enhancement in the clamping force by which the disc is held. The load applied to the motor when moving the clamping member and the turntable away from each other therefore tends to increase. Use of a large-sized motor can cope with an increased load, but being contrary to the demand for reduction in size and weight of the disc driving apparatus itself.